Tomography is a radiological technique which provides a readable image of a plane through a human body while the images of the body structures that lie above and below that plane are blurred. Tomographic images are obtained by a special mechanism that moves an x-ray camera and x-ray film in a manner so that the center of the x-ray beam is always aligned with the center of the film. The x-ray camera and the film rotate, for example, about a center of rotation which lies on the plane to be imaged within the body. In this respect, the x-ray camera and the film describe arcs about the center of rotation, but the plane of the film's surface remains oriented in a position parallel to the plane to be imaged within the body as the film moves in its arc. Thus the plane that passes through the center of rotation and is parallel to the film is recorded on the same area of the film irrespective of the changing position of the x-ray camera; and, the image of the selected plane is thereby distinctly recorded on the film. The images of structures above and below the desired plane, however, are recorded in a series of positions on the film and appear blurred.
Although tomography as described provides the doctor with a capability of taking a look at a cross-sectional slice across the human body, there may be an excessive amount of distortion if the imaging plane through the body is not a true perpendicular or parallel slice through the body member being examined. Thus a circular member may appear in the image as an ellipse and, therefore, cannot be measured accurately. It is a purpose of this invention, therefore, to provide a method and an apparatus whereby cross-sectional views are not only in focus, but can be put in proper perspective and size correctly and without distortion.
Tomographic slices are normally only between 1 to 10 millimeters in thickness. Hence in a large anatomical member a relatively small error in the angle of the film results in an image of only a small portion of the desired slice. Moreover, when the desired slice is missed by the tomographic x-ray because of an incorrect angle, it will very likely go undetected. It is a purpose of this invention, therefore, to provide a method and apparatus whereby a determination can be made of the angle at which an anatomical member should be x-rayed.
Current techniques often necessitate repeated trial-and-error tomographic x-rays to obtain the desired image. The patient, therefore, is exposed to large doses of radiation. Accordingly, it is another purpose of this invention to reduce the patient's exposure to radiation.
An additional advantage of the invention is that prior x-rays can be accurately and easily repeated at a later date (such as after surgery) without again subjecting the patient to additional trial-and-error doses of radiation.
Another problem with tomography is that the mechanisms are so large and bulky that they can't be conveniently moved or repositioned. Hence, the patient must often be physically moved to obtain the desired, angled slices. Consequently, the victim of an accident with a broken neck or other bones may be further injured in the movement or adjustment needed to obtain a cross-sectional tomographic x-ray of the damaged area. In this respect, an additional advantage of this invention is that a patient can be placed in a prone position on a table, for example, and all tomographic x-rays can be taken without having to move the patient, while, at the same time obtaining undistorted cross-sectional images of desired areas.